more sensible display for empty objects and arrays
inlined helpers.withNewContext() in compiled code
displaying a string picks simplest representation
removed some unnecessary parens from compiled code
a few touches in the code that compiles expr nodes
renamed: renderJS -> rhs, renderPatternJS lhs
made first example more illustrative of left-associativity
doctest format: <=> instead of ->
refactored compilation of 'def' nodes